In double walled smoke stacks, which are used to reduce corrosion, an inner shell is exposed to hot flue gases, while an outer shell is not. Thus the inner shell will expand more than the outer one. Clearly, some kind of expansion means is required to prevent the inner shell from buckling or even rupturing as it expands. It is known from U.S. Pat. No. 3,368,506 to provide an expansion means in the form of a V-shaped section and a double flange at the top of the inner shell. However, such a configuration is both heavy and expensive. It is also known from U.S. Pat. No. 3,762,302 to have radially extending members to support a helically wound inner shell, but these members do not allow for expansion.
It is therefore an object of the present invention to provide a double walled expandable smoke stack that is inexpensive.
It is a further object to provide one that is light.